Superlative form of 'chilly,' meaning extremely cold in temperature or extremely unfriendly in mood or manner.
From 'chilly' plus the superlative suffix '-est.' Follows the standard pattern for English adjectives forming their superlative degree.
The superlative 'chilliest' is interesting because it works equally well for weather ('the chilliest day of winter') and for social situations ('the chilliest reception ever')—English reuses cold-temperature words for emotional coldness!
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